Source : Free On-Line Dictionary of Computing

Basic Object System
     
         (BOS) A {C}-callable library that implements the
        notion of {object} and which uses {Tcl} as its {interpreter}
        for interpreted {methods} (you can have "compiled" methods in
        C, and mix compiled and interpreted methods in the same
        object, plus lots more).  You can subclass and mix in existing
        objects using BOS to extend, among other things, the set of
        {tk} {widgets}.  BOS is a {class}-free object system, also
        called a prototype-based object system; it is modelled loosely
        on the {Self} system from {Stanford University}.
     
        Version 1.31 by Sean Levy .
     
        {(ftp://barkley.berkeley.edu/tcl)}.
     
        (1992-08-21)